Not 100% sure if this should go in bug or ux, my apologies if I post in the wrong place.
I opened this link New search operator "not" for tags only - #2 by jomaxro and noticed that a broken thumbnail can cause an annoying issue (tested on Chrome and Edge). A large, broken image. Also you can’t select text or select links under it.
The issue doesn’t show up if I create a new onebox of the same link since the generated thumbnail has a different, working url.
ah ok I see, that’s from the topic New search operator "not" for tags only - #2 by jomaxro
It looks like it might have something to do with our lazyloaded images… it has the correct positioning applied inline (looks like this is all from lazy-load-images.js.es6),
position: absolute;
top: 82px;
left: 28px;
but the width and height are out of whack at
width: 500px;
height: 500px;
I just tried the “rebuild html” option on that post and that corrected it. That post predated our lazyload feature, so I wonder if it was just a fluke when we rebuilt all the posts after that feature was added?
Oh I spoke too soon, now it’s broken in a different way… and it just fixed itself again. Something a bit odd is going on… if I do a hard refresh I will temporarily see the huge image…
@dan it looks like you recently made some changes there… could this possibly be related?
Trying another onebox…
and this is what it looks like in the composer preview
Thanks @Canapin for the report. It is a bug I introduced by mistake after fixing another bug. 
It is now fixed:
https://github.com/discourse/discourse/commit/2d3113e4da74be2a0288dbe3273093cd2d27fd21
